A wide area system protection apparatus is a control device arranged in a power plant or a substation to ensure the stability of a power system when encountering large disturbances. The wide area system protection apparatus realizes machine switching, load shedding, rapid output reduction, urgent rising or descending of DC power and other functions, and is an important facility of keeping safe and stable operation of the power system. A network topology framework of the wide area system protection apparatus generally includes two or more plant stations in communications connection, thereby realizing stable control of regional or a greater range of power systems. Therefore, in order to avoid oscillation problems of a power grid at different frequency bands and facilitate the malfunction analysis, the plant stations need to be kept synchronous in time.
An existing time synchronization method of the system protection apparatus is generally based on a global positioning system (GPS) mode, or a synchronous digital hierarchy (SDH) mode. However, in the GPS mode, once GPS is lost by some plant stations, a global clock synchronization function will be lost, and the related system protection control function will be blocked. In the SDH mode, a special switch that supports SDH transmission and a time synchronization device that supports an IEEE-1588 protocol should be equipped according to an IEEE-1588 time synchronization protocol, which has expensive cost and is not practical.